This invention relates to a novel carbon material, which is obtained by working graphite on the atomic level and can have various shapes and uniquely determined physical properties, and a method of producing the novel carbon material. This carbon material has latent possibilities of wide uses in the next generation industries and particularly in the microelectronic and microoptoelectronic industries.
Well known carbon materials are carbon black, amorphous carbon, glassy carbon, graphite and diamond. The uses of carbon black, amorphous carbon and glassy carbon are limited because these carbon materials have no definite structure. Graphite has a layer structure consisting of regularly stacked uniplanar layers of hexagonally arranged carbon atoms and hence exhibits two-dimensional conductivities. Diamond has a three-dimensional network structure consisting of tetrahedrally arranged carbon atoms. Although the structures and physical properties of graphite and diamond are well known, it is difficult to utilize these carbon materials in electronic devices because there is no method of forming microstructures of graphite or diamond.
A recently discovered carbon material is C.sub.60 which is a spherical assembly of carbon atoms. C.sub.60 exhibits various properties including semiconductivity, conductivity and superconductivity in accordance with its electron structures which are attributed to its symmetries. However, for practical uses of C.sub.60 there is an unsolved problem that variously desired crystals cannot easily be produced.
A more recent discovery is the formation of carbon nanotubes, first disclosed in Nature, Vol. 354(1991), 56-58. A carbon nanotube is made up of a plurality of coaxially nested rolls of graphite sheets each of which has a thickness of several carbon atom layers. The outer diameter of a carbon nanotube is only a few to tens of nanometers, and the length is usually shorter than 10 .mu.m. Carbon nanotubes attracted worldwide attention in view of the possibilities of using as one-dimensionally conducting wires or catalysts or in superreinforced structures. A particularly attractive feature of a carbon nanotube is that the electrical property of each of the nested carbon tubes depends on the tube diameter and the pitch of a helical arrangement of carbon atom hexagons in the rolled graphite sheets and is variable from a metallic conductor to semiconductors with various band gaps. It is intended to use carbon nanotubes as quantum wires, but at present practical use encounters some problems. Carbon nanotubes are always cylindrical, and there is no expectation that carbon nanotubes of a different sectional shape will be produced. Besides, the products of the known methods are always mixtures of nanotubes of various sizes. Although the electrical property of a carbon nanotube strongly depends on its diameter and length, still it is impossible to produce carbon nanotubes with desired diameters and lengths on the order of nanometer.